1,720,957 research outputs found
Thin-target excitation functions: a powerful tool for optimising yield, specific activity and radionuclidic purity of accelerator-produced radionuclides
No full textIn accelerator production of radionuclides, thin-target yield y(EOIB)(E) vs. projectile energy, at the end of an instantaneous bombardment (EOIB), is the slope at the "origin" of the growth curve of the activity of a radionuclide per unit beam current vs. irradiation time, for a target in which the energy loss is negligible in respect to projectile energy. Conversely, thick-target yield Y(E,DeltaE) is a function of particle energy E (MeV) onto the target and energy loss DeltaE (MeV) into target itself, obtained experimentally or by integration of thin-target excitation function y(E). Some local maxima on Y(E,DeltaE) curves are present in many cases. As a relevant conclusion, use of target thickness larger than the "effective" value is unsuitable, due to larger specific power deposited by the beam in target material, instead of cooling system. Moreover, increasing amount of target material leads to a lower value of specific activity, due to larger amounts and volumes of chemicals and equipment. Y(E,DeltaE) curves and their maxima permit calculating optimal irradiation conditions to produce radionuclides with maximum yield, specific activity and radionuclidic purity. In order to join the advantages of accurate knowledge of thin-target excitation functions, very selective radiochemical separations were optimised, without intentional addition of an isotopic carrier
A competitive method for simultaneous deuteron-cyclotron production of No-Carrier-Added copper-64 and gallium-67,66 for applications in PET radiodiagnostic and metabolic therapy of tumours
No full textDetermination of I-125 impurities in [I-123]labelled radiopharmaceuticals, by liquid scintillation counting: sensitivity of the method
No full textIodine-125 is a radioisotopic impurity "always" present in iodine-123, produced by nuclear reactions induced either. on natural or "highly" enriched targets. Liquid scintillation counting is a very sensitive tool to determine low level impurities of both low energy electrons and photons in aqueous and organic solutions of radiopharmaceutical compounds. With this technique it was possible to determine, on commercial samples, that the content of I-125 was of the order of not less than 0.1% for I-123 produced via I-127(p,5n) reactions and not less than 0.01% for I-123 produced via "highly" enriched Xe-124(p,X) nuclear reactions
Preparation of "high specific activity" radiochemical forms of vanadium, manganese and thallium for metallo-toxicological studies
No full textIn this paper are presented the production methods for very "high specific activity" radionuclides (HSA-RN) of vanadium, manganese and thallium which have been developed in our laboratories for labelling different chemical forms of these elements present in the echo-systems in ultra-trace amounts, for metallo-toxicological and bio-kinetic studies. Use was made of both cyclotron and thermal nuclear reactor. If the nuclear reaction product has atomic number different from irradiated target, it is possible separating the radioactive nuclide from irradiated target, without addition of isotopic carrier. This kind of radionuclide is named No Carrier Added, NCA, and his specific activity, A(S) is very high and can reach values close to the theoretical Carrier Free one, CF. The experimental determination of specific activity, chemical and radiochemical purities is mandatory for all these kinds of applications
Thin-target excitation functions and optimization of simultaneous production of NCA copper-64 and gallium-66,67 by deuteron induced nuclear reactions on a natural zinc target
No full textCopper-64 is a radionuclide suitable for labeling of a wide range of radiopharmaceuticals for PET imaging, as well as systemic or local radioimmunotherapy of tumors. Among the possible methods for cyclotron production of No Carrier Added (NCA) Cu-64 (Cu-61), we investigated the deuteron irradiation on natural Zn target, via (d,alpha xn) and (d,2pxn) nuclear reactions. This paper reports the preliminary results about the experimental determination and theoretical calculation of thin-target excitation functions in the energy range up to 19 MeV for Cu-61, Cu-64, Ga-66, Ga-67, Zn-65 and Zn-69m. A fast selective radiochemical separation of NCA Cu-64 from Zn target and Ga radionuclides, with quality control tests is described too
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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